What is aerobic composting
The decomposition of organic matter or biodegradable waste by the action of oxygen-requiring microorganisms is known as aerobic composting.
For large scale composting, many types of aerobic composting processes are followed. some of them are
Types of aerobic composting
- Aerated static pile composting
- In-vessel composting
- Traditional biodigester
- Windrow composting
1. Aerated static pile composting (ASPC):
The process of constructing a large compost pile (heap of compost) over a network of pipelines that help in aerating the compost evenly is known as aerated static pile composting. Unlike in compost bins, this composting is done openly which is covered by a thick layer of mulch to prevent the escape of heat from the pile. The word static itself conveys that there is no turning or disturbing in this composting. Thus easy to maintain. It can be maintained indoors as well as outdoors (depends on the climatic conditions of your area).
All types of organic wastes can be composted. The maximum length of the pile can be 70-80 feet and it produces compost within 3-6 months.
Components of aerated static pile compost :
- Air plenum layer
- Active layer
- Biofiltration layer
Blower: an electric blower (or timer) helps in inducing airflow into the compost pile by triggering the blower fan.
Manifold: a pipe or chamber that has several openings to allow air/liquids to pass through it is known as manifold. A manifold of PVC pipe receives air from the blower and passes it into the compost pile through its perforations.
Air plenum layer: a layer of wood chips, sawdust, or any other material that is spread over the perforations of the PVC pipe to diffuse the air is known as the air plenum layer. This layer helps in the even distribution of air in the compost pile.
Active layer: organic wastes that are composted is known as the active layer. Organic matter that we use should have regular qualities like desired C: N ratio (25-30:1), bulk potential, and moisture content to obtain a good quality compost.
Biofiltration layer: it is spread over the active layer to prevent heat and moisture loss and also helps in protecting the core organic matter from birds, flies, rodents since we maintain it open conditions (not in enclosed bins). This layer can be mulches (straw, grass clippings, etc.), compost, gore covers, or any material that has the mentioned properties. This layer is also known as insulating layer.
Benefits of ASPC:
- Easy to maintain as it can be monitored by the blower timing.
- Need no manpower since there is no turning
- Free of labor cost
- Can be maintained using solar power
- Maintain even aerobic conditions
- Unwanted elements like parasites, pathogens, weeds seeds get destroyed by the heat produced in process of breakdown.
- No bad odours due to the presence of biolayer.
2. In-vessel composting:
The process of composting organic wastes (good/garden/farm/animal waste) in closed chambers/vessels is known as in-vessel composting. Air circulation, temperature, and moisture conditions are completely monitored by forced aeration and mechanical agitations. This type of composting can be done either indoors or outdoors.
The type of enclosed chambers or vessels can be
- Agitated bays
- Rotating drums
- Enclosed halls
In-vessel composting mainly occurs in three stages.
Stage- l: The organic waste is cleaned (materials like plastic, metals will be removed), shredded, and fed into the drum/silo/bay (first barrier) according to the system used and allowed to undergo breakdown. This stage lasts for 1-3 weeks. Due to the heat released in the process of breakdown, the temperature reaches up to 60-70℃. Thus contaminants like weed seeds, harmful pathogens get killed in this stage.
Stage -ll: Now the composting material is transferred to the second barrier, where composting process still continues. This stage ensures whether the waste is completely sanitized or not. Conditions such as temperature, moisture, airflow are also closely monitored at this stage. Air is evenly circulated with the use of buried tubes/agitations. These agitations allow microbes better access to carbon for better decomposition while temperature and moisture are monitored through probes to ensure optimum aerobic decomposition in the barrier.
Stage-lll: After sanitization, the decomposed material is allowed to mature/cure for 10-14 weeks in open windrows or enclosed areas for the stabilization of the compost before the screening. This stage is also known as maturation.
Screening: Screening is done to ensure whether the entire mass is decomposed or not. Any oversize or undecomposed materials will be fed back to the processing system for the complete breakdown. This can be done pre or post maturation to produce a range of product grades, that is suitable for various purposes like soil conditioning.
- Difficult to maintain and requires high operational cost.
- Requires technical skills.
- Training of personnel is needed.
- The size of the vessel limits the capacity of the feed.
3. Liquid food composter (LFC):
LFC is the waste food disposal system that its environment is designed to break down the food waste and bioplastics into drain-safe wastewater within 24 hours with the help of microbes and enzymes. A horizontal agitator (rotating arm) present in the U shaped vessel in this stainless steel unit rotates slowly to maximize the contact between food waste, bacteria, air, water, and proprietary enzymes (residing in the porous plastic chips present in the vessel)
The process of digestion is aerobic and exothermic (releases heat)and automated infusions of hot and cold water fasten the rate of decomposition in the vessel. The nutrient-rich wastewater is eco-friendly that can be either collected (to use for enriching the land) or discharged into drains. All types of food wastes such as vegetables, fruits, rice, bread, noodles, raw or cooked meat, fish, etc.
- Food waste can be added at any time.
- Reduces the CO2 emissions in the environment.
- Can be used in hotels, restaurants, remote areas to dispose of food materials.
- Odour free operation.
4. Traditional Bio-Digester
This bio-Digester usually takes 8-12 weeks for composting and takes only plant-based organic wastes but not animal wastes. These systems use heat oxidation, the name itself expresses that it occurs in the presence of oxygen. The heat produced in the process of decomposing kills the harmful contaminants like weed seeds, pathogens present in the bio-digester.
5. Windrow composting
This method is used for large-scale composting (community level). The Large mass of organic matter is piled into long rows. These long piles are otherwise called windrows. These rows are turned/agitated at regular intervals manually or by mechanical means. Turning is done to distribute moisture, improve aeration, and stabilize the cooler and hotter portions in the windrows.
Organic matter can be farm wastes, yard trimmings, kitchen wastes, animal byproducts (fish/poultry wastes), liquids. The ideal measurement of the windrow is 4-8 feet long and 14-16 feet in width. The windrows are large enough to generate heat and maintain temperature and small enough to allow oxygen flow throughout the pile.
After the decomposition, screening is done to remove unwanted materials (like plastics, metals, etc.) and grade the compost for various end uses
- Suitable for large volumes like waste generated by the entire community, high volume food processing business, (like restaurants, cafeterias, hotels).
- Can be used in gardens, brownfields, landscaping, and agriculture.
- Requires high maintenance as it needs large area, well-built equipment, and man force.
- Leachate needs to be collected and treated. If not collected, it may contaminate the groundwater and surface water supplies
- Associated with strong odours
- Risks of rodents exist.
FAQs Related to Aerobic Composting
1. Is aerobic composting good?
It is the easiest method of composting when compared to anaerobic composting where precautions need to be taken to ensure whether the bin/pile is closed airtight.
2. How do you aerate compost?
Aerating the compost can be as easy as disturbing the materials with a garden fork in the bin to as difficult as it needs machinery or aerating system to turn/agitate the piles.
3. How often should we turn the compost?
Compost should be turned once in 2-4 weeks(depends on bulking potential of wastes and size of the pile/heap). Turning it more frequently doesn’t allow the core of the compost materials to heat up, which is very important to carry forward the process of composting.
4. Can I put food waste like moldy bread, pasta, into the compost bin?
Yes. food materials like moldy bread, pasta, can go into the compost but make sure you bury them deep into the heap to avoid fruit flies and rodents
5. What are the materials that cannot be composted?
If you are trying to making compost at home, it is better to avoid wastes like cooked/raw meat, fish, poultry waste as they may produce a bad smell.
To get quality compost, other materials to avoid are diseased plant wastes, dairy products.
6. What is the ideal pH of a compost bin?
pH range between 5.0-8.0 approximately is ideal for composting as this range supports the microbial activity
7. At what temperature do pathogens and weed seeds get destroyed in the compost bin?
At the thermophilic phase of composting, pathogens (fungal/bacterial spores, eggs, or cysts) get destroyed at 55℃ while weeds get eliminated at 60-65℃.
8. What are windrows in farming?
The elongated piles (row) of composting materials, that are made to partition the large mass of organic wastes to produce compost are knowns as windrows.
9. What are the advantages of aerobic composting?
- Easy to start the process.
- Any organic waste can be composted.
- Helps in fast degradation of materials.
- Minimal odours.
- Reduces the emission of greenhouse gases like methane.
10. What is the ideal C:N ratio for aerobic composting?
The ideal C:N ratio for aerobic composting should be between 25:1 to 30:1. C:N ratio less than the optimum level results in loss of excess nitrogen into the atmosphere in the form of ammonia and nitrous oxide. While higher than the optimum level results in limiting the growth of microbes.
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